Automotive bumpers are subject to a variety of design requirements due to consumer demands, government regulation, and the competitiveness of the industry. Bumpers must maintain a high level of strength and damage resistance to meet consumer expectation and government regulation concerning low speed vehicular impact. However, a bumper must also be of low weight to minimize vehicular dead weight which reduces gas mileage and increases suspension requirements. Also, bumpers must have a low manufacturing cost and high dimensional consistency given the competitiveness of the industry. Thus, high strength-to-weight ratios and ease of manufacture are critical to the success of present bumper systems.
These requirements are further complicated by the present aerodynamic design trends which call for a high degree of sweep across the front of automobiles, such sweep also contributing to the strength of the bumper and its spring-back characteristics.
A variety of designs and methods have been tried to improve bumpers. Many have used new metallic materials (such as aluminum or heat treatable steel alloys) and engineering resins (such as urethanes and elastomers) with varying degrees of success However, many of these new materials suffer from availability and cost problems as well as special processing problems. In addition, where combinations of materials are used, assembly time is increased. Further, the automotive industry continues to demand even higher strength-to-weight ratios.
A conventional bumper has a C-shape formed of relatively low strength and thick steel. Many of such C-shaped bumpers are roll-formed and some are formed with a sweep at the end of the roll-forming operation by passing them over mandrels.
A problem of the traditional, predominant, "C" section bumper is the sudden collapse experienced during deflection when the horizontal flanges give way. The sudden failure makes it more difficult to properly trigger the inflation of air bags which are intended to cushion passengers from secondary impacts during a vehicle crash.
Lastly, bumper attachment methods have become more critical as bumper strengths increase. Forces of impact are larger and transferred more directly.
Thus, it is an intention of this invention to greatly improve strength and reduce weight over present bumper systems while utilizing available materials in a reliable and cost-efficient process of manufacture.
It is a further intention of this invention to provide a bumper which provides its strength and impact resistance over an extended deflection cycle without experiencing the sudden failure experienced by the prevalent traditional "C" section bumpers.
It is also an intention of this invention to provide a method of manufacture allowing a high degree of sweep along the longitudinal length of the bumper, thus allowing for designs which meet the highly aerodynamic designs called for by modern trends and also producing a stronger bumper with improved spring-back characteristics.
It is also an intention of this invention to provide a unique attachment means which will meet the requirements of such a high strength bumper.